This invention relates to a new and improved tubing connector terminal applicable to metal tubing used as a brace, tension link, or tie member in any of a variety of configurations of the tubing serving as an element in passive structures. The invention, in its preferred forms as herein illustratively described, was conceived and developed for tubing used in a number of places and in varying configurations as elements of aircraft jet engine "surrounds" or buildup assemblies that carry, brace or tie down many of the elements auxiliary to the engine within its cowling. The invention is herein illustratively described by reference to its presently preferred embodiments for such purposes; however, it will be recognized that modifications and changes therein may be made without departing from the essential features involved.
Conventional practice for years in providing tubing used as an element in passive structural applications has been to flatten the tubing end to form a dual wall thickness, single-plane cross section termination that could be drilled for bolting or riveting or that could be welded in face-to-face contact with an opposing flat surface of another element in the passive structure. While an acceptable technique for many applications, the former practice has been recognized in others as unreliable, due to early and often totally unexpected structural fatigue failure of the connector terminal. Such fatigue failure was found to occur in the single-plane cross section region of the terminus. In addition, the single-plane cross section terminus would not carry loads in bending, and it left considerable offset between the contact face of the terminus and the adjacent side tangency plane of the tubing precluding or making it difficult to position the tubing side against and along the other member to which it was fastened. In consequence, the potential advantages offered by the use of tubing in passive structures, namely strength combined with lateral stiffness, lightness of weight and cost-effectiveness, otherwise continuing to favor its use where possible, particularly in aircraft structures where those qualities are critically important, were not consistently available to the structure's designer.
In addressing the problem, it was noted in accordance with this invention that fatigue failures in the single-plane cross section of the flattened tubing end even occurred in applications wherein the tubing side cleared the adjoining member and the fastener means between them was ostensibly loaded in pure shear by the tubing.
The principle object of this invention is to provide an effective solution to the described problem, namely, avoidance of tubing terminal connector fatigue failure; also avoidance of the former restrictive limitations on the use of tubing as elements in passive structures. In addition, auxiliary advantages are afforded; in particular, stiffness and strength against transverse bending loads should they also have to be carried by the tubing connector terminal.
The improved connector terminal, apart from static or passive structure loading also is much more durable and fatigue-free to withstand vibrational load stresses as occur in aircraft engine auxiliary structure applications and similar uses, this representing a highly important additional advantage.